The invention relates to a digital recording and reproducing system, and, in particular, a record carrier for use with that system. More specifically, the record carrier is of a type that can be used with a system comprising a device for recording a digital electric signal in a longitudinal track on the record carrier and a device for reproducing the digital electric signal from the track on the record carrier. The recording device of such a system can receive the digital electric signal with a specific sample rate, convert the digital electric signal into a form in which it can be accommodated in consecutive frames at a specific bit rate and record the frames in the track on the record carrier, thereby producing a record carrier having a longitudinal track with frames included therein. The reproducing device of such a system can read the frames from the track on the record carrier and decode the information contained in the frames to produce a digital electric signal having substantially the same sample rate.
A recording and reproducing system of the type described above (which can be used with a record carrier of the type described above); is known, for example, from the book "The art of digital audio" by J. Watkinson, Focal Press 1988, Chapter 9. Chapter 9.20 of that book describes, for example, a system, known as SDAT. In that system a digital signal is recorded in a plurality of juxtaposed tracks formed, or to be formed, on a record carrier in the longitudinal direction of the record carrier. The recording device in that system is intended for recording a digital signal, such as a digital audio signal originating from a digital signal source such as a Compact Disc (CD) audio player, on the record carrier. For that purpose, the digital signal having a specific sample rate fs, which is fs=44.1 kHz if the digital source is a CD audio player, is applied to the recording device. In the recording device, the digital electric signal is converted into a form in which it can be recorded on the record carrier. Recording in the tracks is effected at a bit rate which is neither equal to nor locked to the sample rate fs. For that purpose, the recording device comprises a separate frequency source (crystal). However, a problem may arise because the sample rate at which the digital electric signal is applied to the recording device varies. Moreover, the frequency supplied by the frequency source may vary. The last-mentioned frequency variations may be caused, for example, by temperature fluctuations affecting the frequency source.
The recording device of the system described in the Watkinson book also has an analog input. An analog electric signal applied via that input is sampled at a sample rate of 44.1 kHz and is digitized. In order to enable the analog signal to be sampled at 44.1 kHz, it is generally necessary to have a second frequency source (crystal) to supply the sampling frequency of 44.1 kHz. However, the frequency supplied by the second source may also vary. If the digital signal is to be recorded correctly on the record carrier, the variations in the sample rate and the clock frequency of the first-mentioned frequency source should be allowed and compensated for.
In the prior-art devices, this is realized, inter alia, by loading the samples of the digital signal, which are received with a variable sample rate, into a memory and by reading them out of this memory at a fixed frequency. Moreover, transport speed control is applied to compensate for the variable bit rate with which the signal processor in the recording device supplies the information in the frames for recording on the record carrier.